Effects of charge carrier behaviors on the time response of CdZnTe crystals irradiated by pulsed X-rays

As-grown high resistive CdZnTe crystals were employed to fabricate planar detectors. The pulsed X-rays induced transient current waveforms were obtained at room temperature. The rise time and decay time of the transient currents were evaluated. The rise time is approximately of 2 ns, which is independent on the bias voltage. The current decay can be divided into 3 parts. The charge transport behaviors were analyzed using α particles induced pulses combining with time of flight technique. The effects of structure defects on the charge carrier scattering and trapping-detrapping were discussed. In addition, the transient current waveforms of CdZnTe detectors with different thickness were compared as a function of bias voltage. The full wave at half maximum (FWHM) of the transient currents is exponential decay as the bias increases. However, the variation is limited when the detector is thicker than 0.2 mm, which is possibly attributed to the increasing trapping and scattering centers in the materials. Thus, the charge transport properties were degraded and the recombination time was prolonged.